The present invention relates to machines for finishing metal workpieces, e.g., for milling and then grinding a surface of the workpiece.
Machines for simultaneously milling and grinding a workpiece are known. Such a machine is disclosed, for example, in U.S. Pat. No. 5,285,600, which comprises a cutting ring having milling inserts mounted thereon, and a grinding wheel disposed coaxially inside of the cutting ring. The milling ring and grinding wheel are driven at different respective speeds about a common axis of rotation by means of respective drive motors. That machine can be employed to machine portions of metallic engine blocks, among other uses.
However, the machine exhibits certain shortcomings, one occurring when the machine is used to form a surface intended to support a steel sealing gasket. Steel gaskets are of less flexibility than other types of gaskets, e.g., fabric or rubber gaskets, whereby the surfaces between which the steel gasket is to be clamped must be highly smooth in order to prevent leakage. A surface cut by a rotary milling cutter will exhibit a "waviness" due to the creation of curved rings or scallops across its surface. The rings define grooves which enable fluid to leak past a steel gasket. The use of a coaxial grinding disc as described in the above-referenced prior art machine will reduce the height of such rings, but possibly not sufficiently to eliminate the need for performing an additional polishing step.
A second shortcoming of the above-described machine is evident in situations where the machine is used to finish a workpiece surface which terminates at a corner or shoulder defined by an upstanding wall of the workpiece, and wherein it is necessary that the surface be ground essentially right up to that corner. The milling cutters can be brought right up to the corner, but the coaxial grinding wheel cannot, due to the radial spacing which must be provided between the milling cutters and grinding wheel to allow the grinding wheel to rotate within the milling cutter. Hence, a separate grinding step may have to be performed to finish the surface right up to the corner.
A third shortcoming of the above-described prior art machine relates to a need to periodically adjust the axial relationship between the milling cutters and the grinding wheel as the milling cutters wear. In that machine, the axial adjustment is made by axially displacing the milling cutter relative to the grinding wheel. In particular, a cylindrical slide which carries the milling cutter spindle (which, in turn carries the milling cutter) and rotary bearings which support that spindle, are axially displaced by a hydraulic positioner. However, the bulk and weight of the slide, spindle, bearings and milling cutter make it difficult to achieve the required fine adjustments of the milling cutter.
Therefore, it would be desirable to provide a milling/grinding machine which eliminates the above-described shortcomings. It would also be desirable to increase the life of the spindle and bearings which support the grinding wheel, and to render the machine more compact in size and less costly to make.